Call them. If a phone is IMEI blocked, it's blocked at the carrier's end/network & unable to use their network, and in many countries, other carriers networks in that country (and also quite possibly networks in other countries). So as it's not something that's blocked phone-side, nothing anything here can do to solve this.
If it's important enough to cause you grief if it's lost, back it up. No excuses
Trolling for thanks is lame
Does Samsung's auto-brightness implementation crap drive you to self-harm ? A solution !
Failure to search is the leading cause of male impotence on XDA
If you don't know how to recover if things go wrong, what are you doing flashing custom roms ?